| With the energy crisis and environmental pollution caused by the increasingly exhausted fossil-fuels,among many clean energy sources,hydrogen has become the most ideal traditional energy substitute due to the advantages of high energy density,environmental-friendliness,zero-pollution and renewability.Electrocatalytic hydrolysis based on a coupled pair of cathodic hydrogen evolution?HER?and anodic oxygen evolution?OER?is considered to be the most promising and green approach to hydrogen production.Currently,the best catalysts for HER and OER are precious metals Pt/C and Ir?Ru?O2 respectively,which have limited commercialization due to their low earth-reserves and high-costs.Transition-metal-based composite energy materials with the merits of tunable d-electronic structure,rich raw-materials and diverse valences etc.,become the most excellent and promising candidates.Herein,we engineered reasonably and prepared a series of real ultra-highly efficient and remarkably durable transition metal hybrid electrocatalysts for electrocatalytic HER and OER.The main contents were as follows:?1?Preparation of S-doped NiCo composite material as a highly-efficient electrocatalyst for hydrogen evolution reaction.One of the enormous challenges for developing renewable hydrogen sources of electricity-driven water-splitting systems has been limited by earth-abundant and robust highly-active cathode electrocatalysts.In this work,we developed a simple sulfur-anion doping strategy to obtain S-doped NiCo composite?S-NiCo@50?on Ni foam?NF?via a one-step electrochemical deposition.The doped sulfur amount is discussed,finding that doped sulfur plays a crucial role for reducing overpotential of hydrogen evolution due to providing abundant active sites by XPS spectrum identified.Meanwhile,formed metallic Ni and Co effectively promote electron transportation.The synergy effects between the amorphous CoxNiyS?x+y?substance and crystalline Ni and Co metals seem to result in enhanced HER activity.Especially,S-NiCo@50 electrode,feature with a hierarchical morphology,shows an ultralow overpotential of 28 and 125 mV at 10 and 100 mA cm-2 in 1.0 M NaOH respectively,with a large exchange current density?j0?of 4.8 mA cm-2 as well as high conductivity and stability,whose catalytic property is superior to the most of reported alkaline electrocatalysts,even on par with commercial Pt/C.Assembled with counter electrode?Ni-Fe/NF?,the overall water splitting is proved with a low 1.55 V at 10 mA cm-2.Moreover,we built the Ni24Co6S6 cluster as the S-NiCo@50 model and revealed its intrinsic activity by density functional theory?DFT?calculations.This study shows S-doped and component control can be an exquisite strategy to realize high-efficiency water electrochemical reduction.?2?Controllable synthesis of amorphous?Ni-Fe?Sx/Ni Fe?OH?y hollow microtube/sphere films as superior bifunctional electrocatalysts for quasi-industrial water splitting at large-current-density.Crystalline transition-metal chalcogenides with?oxy?-hydroxides hybrids multiple nanoarchitectures are a new type of promising bifunctional electrocatalysts for electrolysis of water,but their amorphous states are scarcely studied.Herein,a facile electrodeposited approach is presented to fabricate hierarchically amorphous?Ni-Fe?Sx/NiFe?OH?y films on Nickel foam.By accurately tuning multi-components and electrochemical-parameters resulting in abundant micro-tube/sphere morphologies and phase evolution to obtain unique amorphous nano-cluster architectures,the?Ni-Fe?Sx/NiFe?OH?y catalyst performs super electrocatalytic performance,driving the current density of 100 mA·cm-2 at ultralow overpotential of 124 mV and 290 mV for hydrogen and oxygen evolution reaction in 1M KOH solution with first-class long-term stability for at least 50 h,respectively.In addition,the bimetallic Ni-Fe sulfides and Ni Fe hydroxides are confirmed to be highly-intrinsic active components for HER and OER.More importantly,the?Ni-Fe?Sx/NiFe?OH?y material directly as cathode and anode electrodes,achieves 10mA·cm-2 at low electrolytic voltage of 1.46 V in 1 M KOH,even at large current density of 1200 mA·cm-2 only needing 2.2 V as well as super-durability at 1000mA·cm-2 for 50 h in quasi-industrial conditions.Further experimental results reveal that both temperature and appropriate alkalinity are in favour of reducing the overall hydrolytic overpotential due to accelerating sluggish thermodynamics and dynamics.Parallelly,the bifunctional?Ni-Fe?Sx/NiFe?OH?y electrode is one of the best efficient electrocatalysts in alkaline electrolyte up to now and expected for large-scale industrial water-splitting at large-current-density.?3?Assembling amorphous?Fe-Ni?Cox-OH/Ni3S2 nanohybrids as an ultra-highly efficient electrocatalyst:inner investigation of mechanism for alkaline water-to-hydrogen/oxygen conversion.Rational design of earth-abundant electrocatalysts with ultra-high activity and durability for the electrochemical water-to-energy conversion systems is still a significant challenge.Herein,a hierarchical nanocluster hybrids of trimetallic?Fe-Ni?Cox-OH nanofilms decorated amorphous Ni3S2 with S-vacancy supported on nickel foam?NF?was proposed via rapid two-step electrodeposited pathway.By effectively breaking long-range-order of Ni3S2 to form S-vacant amorphous phase,combining with the strong electronic interactions between the?Fe-Ni?Cox-OH and Ni3S2,it resulted in favorable water adsorption ability,free-energy of H*adsorption(?GH*),and fast mass/charge transfer for hydrogen evolution process.The?Fe-Ni?Cox-OH/Ni3S2 nanohybrids displayed ultralow overpotential of 91 and 145 mV at 100 and 1400 mA·cm-2 respectively with admirable durability for 100 h at 200 mA·cm-2 in 1 M KOH,even exceeding Pt plate.The amorphous S-vacant Ni3S2 plays a crucial role for hydrogen evolution:compared with both original and defective Ni3S2,the free energy of disordering Ni3S2 for*H-OH and H*intermediates more tend to thermodynamical neutrality according to density functional theory?DFT?calculations.For water-to-oxygen evolution(?100=280 mV),in situ newly formed ultrathin NiOOH nanosheets on near-surface Ni3S2 layer coupling with?Fe-Ni?Cox-OH nanofilms can be identified as intrinsic OER active species;and the host metallic Ni3S2 phase provides wonderful conductivity.Impressively,the bifunctional?Fe-Ni?Cox-OH/Ni3S2 nanohybrid represents the best electrocatalyst so far,achieving cell-voltage of 1.45 and 1.61 V at 10 and 200 mA·cm-2 respectively with super stability for 100 h.?4?Synthesis of in-situ core-shell interlink ultrathin-nanosheets Fe@FexNiO/Ni@NiyCoP nanohybrid by scalable layer-to-layer assembly strategy as an ultra-highly efficient bifunctional electrocatalyst for alkaline/neutral water reduction/oxidation.One of tremendous challenges for industrially profitable water electrolysis by a most economically viable electrochemical approach is to exploit earth-abundant and ultra-efficient bifunctional?pre?electrocatalysts.Herein,a scalable layer-to-layer assembly strategy is firstly proposed to delicately construct in-situ core-shell Fe@FexNiO nanospheres interlink ultrathin Ni@NiyCoP nanosheets nanohybrids on Ni-foam via controllable two-step electrodeposition pathway.By deliberately introducing metallic Fe and Ni into amorphous FexNiO/NiyCoP nanoclusters serving as everlasting-conductivity and attached-active-sites along with morphological controls,the Fe@FexNiO/Ni@NiyCoP nanohybrids achieved ultralow overpotential of 92 and 270 mV at 100 mA·cm-2 for electrocatalytic hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?with uncompromising long-term durability for 100 h in 1 M KOH alkaline-electrolyte,respectively,even superior to Pt plate and RuO2 at larger current density(?=400 mV,?=129 mV at 1500mA·cm-2).Besides,it also expressed wonderful catalytic activity in 1 M phosphate-buffer-solution?PBS,pH=7?,achieving cell-voltage of 1.86 V at 10mA·cm-2.The metallic Ni bonding amorphous NiyCoP was recognized as high-intrinsic HER activity,whereas the Fe@FexNiO coupling in situ newly generated NiCoOOH species on the Ni@NiyCoP surface-layer were identified as intrinsic OER performance;the synergistic effects of Fe@FexNiO and Ni@NiyCoP further accelerated water splitting dynamics.Impressively,the bifunctional Fe@FexNiO/Ni@NiyCoP/NF achieves alkaline cell-voltage of 1.43 V at 10 mA·cm-2,representing the best bifunctional material hitherto,which is promising for scale-up commercial the production. |
PDF Full Text Request